Image sensors have become ubiquitous. They are widely used in digital still cameras, cellular phones, security cameras, as well as, medical, automobile, and other applications. The technology used to manufacture image sensors has continued to advance at a great pace. For example, the demands of higher resolution and lower power consumption have encouraged the further miniaturization and integration of these devices.
Semiconductor device performance (including image sensor device performance) is directly related to the types of metal-semiconductor junctions employed within the device. Depending on the different pieces of circuitry being electrically contacted, many different material compatibility related issues may arise. For instance, one piece of device architecture may require a relatively high charge carrier density to move through it during device operation. In this situation, it may be advantageous to tailor the choice of material or device dimensions to best match the specific performance requirement.
Contact resistance refers to the resistance attributed to the interfaces between touching electrical leads (as opposed to the intrinsic resistance of any one part in the system, which is an inherent property). Similar to tailoring specific pieces of device architecture to meet specific performance specs, electrical contacts may have to be tailored to have specific properties. In some situations failure to optimize electrical contacts may lead to diminished device performance and possibly critical failure.
Corresponding reference characters indicate corresponding components throughout the several views of the drawings. Skilled artisans will appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help to improve understanding of various embodiments of the present invention. Also, common but well-understood elements that are useful or necessary in a commercially feasible embodiment are often not depicted in order to facilitate a less obstructed view of these various embodiments of the present invention.